As electronic devices continue to become more feature rich, the extra functionality typically requires the addition of circuitry to the electronic devices. The additional circuitry being added to the electronic devices usually takes the form of integrated circuits, be it in the form of extra integrated circuits or revisions of existing integrated circuits with more functional parts. While integrated circuits typically offer enhanced reliability and lower power consumption over discrete components, the addition of extra integrated circuits usually means that the electronic devices will incur an increase in power consumption. Increased power consumption may be undesirable, especially for wireless electronic devices, e.g., cellular telephones, personal music players, etc., where the increased power consumption may decrease the operating time between battery charges.
In an electronic device with a wide array of features, only a few of the features may be in use at any given time. For example, in a smart communications device containing a cellular telephone, a web browser, a personal digital assistant, a pager, a multimedia player, a navigation device, and so forth, the use of a single feature often precludes the use of many of the remaining features. For example, when a user is speaking on the cellular telephone, it may be that the multimedia player and/or the browser and/or the navigation device will not in active use. Therefore, power may be reduced or turned off for integrated circuitry implementing the features not in use to help reduce power consumption.
One approach commonly used to help reduce power consumption in an electronic device is partitioning of integrated circuits in the device into power domains. When a circuit in a power domain is needed, then all circuitry in the power domain is powered. If no circuitry in a power domain is needed, then none of the circuitry in the power domain is powered. Enhancements to this approach add hierarchical power domain trees to increase control over which circuits to turn on and which to turn off, while other enhancements have helped to resolve signal routing problems and power rail stability. Partitioning of circuits into power domains and the addition of power control hardware for the domains may significantly complicate the design and development process as the partitioning into power domains may adversely affect wire length, area, and timing in an electronic device.